A compound anchor of the above kind is known from the British patent 953,056 and comprises a glass cartridge filled with cement, plaster, lime or another dry mortar and also a brittle inside container encasing water and any rapid-curing means dissolved in it. The rear aperture of the cartridge is hermetically sealed by a cover. A plastic stopper with a central orifice is mounted on the cover and rests externally against the borehole wall. This known compound anchor is laborious or disadvantageous in that, to close the cartridge using a hermetic cover, several time-consuming operations are required. Substantial forces being exerted by the rotationally driven anchor shank, there is danger that the foam adhering to the rupturing cover parts shall tear and that as a result the thin cement mixture no longer shall be adequately sealed. Even when the borehole is horizontal, it must be expected that water shall drain from the inside container through its first-destroyed end, i.e., there shall be excess water at the entry of the borehole, the powder cement mortar remaining dry from the middle to the bottom of this borehole. The problem of incomplete mixing of the binder is more acute yet with any up-slanting, and most of all with vertical, upward boreholes. There is strong expectation in all these cases that the anchor shank shall fail to be firmly bound into the borehole in the light of the thin cement slurry caused by excess water and draining from the borehole on account of a tearing plastic stopper when the seal is destroyed.